Chameleon Arch
The Chameleon Arch was Time Lord technology which could modify the biology of an individual, essentially changing that individual's species. Connected to a TARDIS's databank via a cable, the arch resembled a headset incorporating a bio-data module usually resembling a fob watch. The module was placed on the front on the Time Lord's forehead. The watch stored the Time Lord's essence and when opened, would return it to the Time Lord. The arch gave the Time Lord a new personality and memories. To ensure that the bio-data module would not be noticed, it was incorporated with a perception filter. Using the arch re-wrote a Time Lord's cellular biology and was therefore painful. The Tenth Doctor screamed in agony when undergoing transformation into a human. It was capable of altering them both with or without modifying their outer appearance. Function Some traits of the user's true Time Lord self still remained after the use of the Chameleon Arch. For example, John Smith was able to use a simple cricket ball to deliberately cause a complex chain of events to save a mother and her baby from being crushed by a falling piano. Smith also kept a dream journal in which he chronicled memories of the Doctor's adventures. Professor Yana heard drums beating in his head all his life, a burden the Master also faced. The Eighth Doctor claimed that destroying a Chameleon Arch while the user was not a Time Lord would render their Time Lord personality and biology irretrievable. Notable uses There was an account suggesting the Seventh Doctor, prior to his regeneration into his eighth incarnation, made use of a broken Arch to create the fiction that he was half-human to use against the Master. The Time Lord who would become Quarren Maguire was a powerful psychic with a great potential to manipulate reality, but he used the Chameleon Arch to escape the Time War as he didn't want to fight, hiding his Time Lord self in a locket that he shared with his wife, Rupa Maguire. After the Daleks attempted to track him down, his identity was exposed by Ollistra while he was attempting to escape with various other human refugees in the TARDIS. Lost for options, Maguire opened the Arch and restored himself to his original state, rewriting reality to save the TARDIS and send most of the human refugees to safety- although he left the Eighth Doctor with the company of his new acquaintance Bliss to act as his new companion- while sending the other Time Lords away from the TARDIS. This action also erased his entire human life from history, with the result that Rupa no longer had any memory of meeting him or their marriage. The Master also used the Arch to turn into a human infant to escape the Last Great Time War, after witnessing the Daleks take over the Cruciform. He remained in human form for long enough to grow into adulthood and even old age until he opened the bio-data module and remembered who he was. The Ninth Doctor gave a biodata module to Plex. The Tenth Doctor used a Chameleon Arch to change himself into the human John Smith to elude the Family of Blood. The Tenth Doctor used a representation of his Chameleon Arch to recover his memories, after his mind was taken over by Es'Cartrss of the Tactire. The Tenth Doctor also briefly considered that Jackson Lake might be a future incarnation of himself under the influence of an Arch. Lake had what turned out to be just an ordinary fob watch. The initials on the back of the fob watch revealed his true identity to both himself and to the Doctor. Known Chameleon Arches During the Last Great Time War, the extremely psychic Time Lord who would adopt the name Quarren Maguire used a Chameleon Arch to make himself human, fearing his abilities would be used for the destruction of more than just the Daleks. His bio-data module took the form of a pendant. Following the disappearance of Gallifrey, there were only two known Chameleon Arches in the universe. One belonged to the Doctor inside his TARDIS, though he gave the bio-data module fob watch to Timothy Latimer. In light of its later appearance in the Eleventh Doctor's drawing room, he seemed to have either recovered it or had duplicates, as the Ninth Doctor gave a modified one to Plex that broke down by the time the Twelfth Doctor retrieved it. The other was in the possession of the Master before he left the end of the universe for the 21st century.